1. Technical Field
The present invention relates in general to an improved disk drive, and in particular to an improved apparatus and method for depopulating a head stack assembly in a disk drive by utilizing an overmolded actuator.
2. Description of the Prior Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly, sometimes referred to as the head stack assembly, is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
For some applications, such as disk drives with fewer disks, a head stack assembly having a lesser number of arms is needed. In these situations, the manufacturing techniques typically require separate tooling, such as stamping and molding dies, for each different type of head stack assembly. Such tooling is quite expensive and can significantly affect assembly line flexibility. Thus, an improved apparatus and method for increasing head stack assembly flexibility while reducing the costs of manufacturing is needed.
One embodiment of a head stack assembly for a hard disk drive comprises an actuator comb body, a coil yoke, at least one actuator arm, and a prosthesis. The prosthesis is an artificial or replacement arm for the actuator arm and is preferably identical in profile and thickness as the actuator arm, except for some or all of the balance holes in the actuator arm. This configuration eliminates the need to provide the prosthesis with a real or dummy head in order to balance the actuator, thereby reducing cost. A common stamping die and a common molding die are used for both the arm and the prosthesis, which further reduces the cost of manufacturing. In addition, the invention allows for common usage of assembly tools in the hard disk drive assembly line.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.